The Iowa State University FAPRI Trade Model

International Relations/Trade,

Speech Sensorimotor Learning through a Virtual Vocal Tract

Studies of speech sensorimotor learning often manipulate auditory feedback by modifying isolated acoustic parameters such as formant frequency or fundamental frequency using near real-time resynthesis of a participant\u27s speech. An alternative approach is to engage a participant in a total remapping of the sensorimotor working space using a virtual vocal tract. To support this approach for studying speech sensorimotor learning we have developed a system to control an articulatory synthesizer using electromagnetic articulography data. Articulator movement data from the NDI Wave System are streamed to a Maeda articulatory synthesizer. The resulting synthesized speech provides auditory feedback to the participant. This approach allows the experimenter to generate novel articulatory-acoustic mappings. Moreover, the acoustic output of the synthesizer can be perturbed using acoustic resynthesis methods. Since no robust speech-acoustic signal is required from the participant, this system will allow for the study of sensorimotor learning in any individuals, even those with severe speech disorders. In the current work we present preliminary results that demonstrate that typically-functioning participants can use a virtual vocal tract to produce diphthongs within a novel articulatory-acoustic workspace. Once sufficient baseline performance is established, perturbations to auditory feedback (formant shifting) can elicit compensatory and adaptive articulatory responses

Associations Between Climate, Latitude, Fertility and the Decline of the US Sex Ratio at Birth

The US sex ratio at birth (SRB) has declined since 1970, while ambient temperatures have been increasing. This study examines the temporal and spatial variation of the US SRB from 1979–2002 in association with fertility rates and climate variables. Approximately 62.8 million birth records from the National Center for Health Statistics were linked to monthly climate division data and county level socioeconomic variables to evaluate the association of SRB and environmental conditions at or near the time of conception. Seasonal variation in US SRB is detectable in time series analysis, and is somewhat in phase with variation in fertility. Logistic regression analysis shows that temperature in the month before conception is significantly positively correlated with the likelihood of a male birth when birth order, maternal age, maternal education, plurality, gestation length, race, and Hispanic origin are controlled. This association was significant in models that include all births from 1979–1988, non-Hispanic white births from 1979–1988, and all births in US large counties from 1979–2002. Geographic nonstationarity of US SRB was found in smoothed rate climate division maps for 1979–1988, with higher SRB in latitudes below 40 degrees N, especially in the southeastern US. However, both the overall rates of summer conception and the likelihood of summer male conception are reduced in lower latitudes relative to higher ones. A logistic regression model was also fit using only non-Hispanic births from US large counties from 1989–2002. In addition to a significant positive association of sex ratio and temperature in the month before conception, deviation from normal monthly temperature during the month of conception, compared to the 1971–2000 baseline temperature, is significantly associated with sex ratio variation. In this population, fewer males were conceived when temperature extremes were significantly above normal; more males were conceived when temperatures were significantly below normal. In both high and low latitude zones over this period, the peak of male conceptions shifted to earlier in the year. Variation in SRB is potentially a sentinel health event and this research suggests that the association between temperature and SRB should be integral to any study of SRB variation across large geographic areas or long time periods

Toward a Geography of Hormones: The Human Sex Ratio at Birth in the United States 1970-1995

It has been hypothesized that humans may exert facultative, adaptive control over their sex of their offspring through the action of the endocrine system. No conclusive evidence of this has been found, although varying hormonal levels in parents at the time of conception may partly influence the sex of the child (James 1986, 1987b, 1999). A decline in the human sex ratio at birth (SRB) observed in the U.S. and some other countries has been attributed by some investigators to widespread environmental exposure to endocrine disrupting chemicals. The many factors hypothesized to influence the SRB make testing this attribution difficult, but one suggestion has been to explore the geographic and temporal pattern of SRB to determine if a sentinel health event signaled by abnormal SRB is present (Davis et al. 1998). This thesis explores the possibilities of geographic analysis of SRB at various scales, focusing on the local geographic scale of the U.S. county to determine whether patterns of explainable variation exist. It tests the basic geographic-patterning assumption, the hypothesis that hormonal mediated influences such as local socioeconomic conditions, adult reproductive sex ratio, urban versus farm environment, and racial composition may influence the SRB, and looks for posited geographic patterning that might be indicative of hormonally active agents working in the human environment. This set of hypotheses is tested in univariate and multivariate logistic regression models combining complete U.S. individual birth record datasets for 1970, 1980 and 1990 with selected U.S. Census county-level statistics that were chosen to represent hypothesized socio-environmental, hormonally mediated influences. Separate models were constructed for white and black births, and variables of birth order, plurality, and seasons of birth were included in multivariate models to control for these confounding individual influences on the SRB. Results show that geographic patterning is strongly evident at the county level and this approach in general works well to elucidate the influence on SRB of these external hormonally medicated factors. SRB in white populations significantly decreased with increases in county urban population proportion in 1980 and 1990 and with increases of the percentage of families living below the poverty line in 1970 and 1990. The change in odds ratio for white male births was barely detectable, however, and was less than that found for individual characteristics such as birth order and plurality. Black population SRB was not as influenced by externally hormonally mediated factors as white SRB, except in 1980. Little clear evidence for the presumed effects of endocrine disruptors was found. The results support further study of externally hormonal mediated influences on the SRB at local geographic scales. In particular, geographic patterning is strongly evident but varies locally in magnitude and sign, and spatially in pattern, between sampling dates. This suggests that not all significant factors are accounted for in this analysis, and that more work needs to be done to weigh the independent influences of individual biological factors and those external factors that might vary with changes in social, economic, and age-distribution conditions. A significant influence of SRB seasonality in the 1970 sample year also suggests that changes in temperature, light, rainfall patterns and other environmental signals that might stimulate hormonal influence of the SRB should be explored